Excel 2007 : Formula to Differentiate Empty Cell from Cell returning Blank as result

Hi, the question may be slightly confusing....

-------- A ----------B
1 ------ 3 --------- 15
2 ------ 0 --------- 0
3 ------ 7 --------- 35
4 ------ 2 --------- 10
5
6

For example, the formula from B1:B4 = (INDEX(A:A,ROW())) *5 i.e B1 = A1 *5
As you can see, Row 2 returns a "0" via formula, while Row 5 & 6 are blanks

I wanted a formula to display the row number of the last row that contains formula in Column B, which should be "4" in the example.

Is there a way to do that? Thanks in advance!

You could perhaps use MATCH

=MATCH(9.99E+307,B:B)

Regards B1:B4 - why not just use: =A1*5 ?

If you're getting an #N/A then you have no numbers in Column AK (previously we were looking at formula in Column B which returned numbers)

Rather than entering a game of 20 questions I'd suggest posting a sample that reflects set-up and requirements.

Given you're now dealing with text strings (ie Null return or text):

=MATCH(REPT("Z",255),B:B)

Wow.. it works nicely.
Thanks for the help!

EDIT: Although I still don't really understand the logic behind